I used to run 10.3 for a short while on a 300Mhz iBook G3, it wasn't great, it used up 2/3rds of the available HDD space but it worked
I think Arduino 0009 will work on 10.3.9, not sure about the newer versions though
Maybe it's time to have a scout around ebay? Or perhaps get a cheap old PC and run Ubuntu to keep things simple, you may even get lucky and find someone giving away old hardware in the next few weeks.